A Research Paper Published in Crystal Growth & Design

The research was focused on studying to what extent isomorphism of the coformers will induce isomorphism of halogen bonded cocrystals. A series of 12 N-(4-halobenzyl)-3-halopyridinium halogenides, 11 of which are isomorphous, have been crystallized with a neutral halogen bond donor, 1,4-diiodotetrafluorobenzene. A total of 18 crystalline products were obtained, 13 of which were 1:1 cocrystals, three 2:1 cocrystals, and two 2:3 cocrystals. The two 2:3 cocrystals were isomorphous, while the 1:1 cocrystals constitute seven structural types, four of which correspond to isomorphous series, and the 2:1 cocrystals two types, with one isomorphous pair. There does not seem to be any simple relation which would translate the crystal isomorphism in a series of coformers into the isomorphism of their respective cocrystals. For the cases where both the coformers and the cocrystals were isomorphous, discernible correlation between the corresponding isostructurality indices could be observed. On the other hand, taking into consideration that the dominant directional interaction in all the structures was halogen bond, a number of regularities can be observed, indicating that the distribution of the cocrystals among the structural types is to a large extent determined by the halogen bonding potential of the constituent cations and anions. The research was performed as a part of the research project New building blocks for the supramolecular design of complex multi-component molecular crystals based on halogen bonds (HaloBond IP-2019-04-1868) funded by the Croatian Science Foundation.